Eccentrics have long been used for converting rotary motion into reciprocatory motion and vice versa. Varialbe eccentrics generally consist of two juxtaposed, eccentric members mounted on a drive shaft. As the outer eccentric is rotated about the inner eccentric, the eccentricity changes. If both members have identical eccentricity, the eccentricity may be varied from zero to a maximum and back to zero. Locking of the eccentric members in normally accomplished with pins, locks or bolts. A method for varying the throw of the eccentric while it is in rotary or angular motion is taught in U.S. Pat. No. 4,249,424, issued to William J. Glazier on Feb. 10, 1981. Glazier uses a geared control shaft which is coaxial with the drive shaft and which is coupled through an idler gear to gearing on the inner surface of the outer eccentric.
A variable-throw eccentric constructed from two juxtaposed eccentric members necessarily undergoes a phase change through 180 degrees as the outer eccentric is rotated. This characteristic complicates the design of pumps, motors or engines which rely of sychronized valve timing. A variable-throw constant-phase eccentric would be advantageous in such applications.
In pump, motor or engine applicaions, a variable-throw eccentric poses an additional problem. As the stroke is reduced, the compression-ratio is also reduced. Efficient use of the variable-throw eccentric in such applications would neccessitate the development of a means for maintaining a constant or nearly-constant compression ratio as the stroke is changed. A pump, motor or engine with varialbe stroke and constant compression would actually be able to "shrink" as the load or output requirements varied. The shrinkage would reduce friction and thermal losses. A primitive attempt at shrinking an engine as the load decreased was made by General Motors Corporation. In the early eighties, certain cadillac automobiles were equipped with V-8 engines in which the intake valves of up to four clinders could be deactivated as the load on the engine decreased. Of course, deactivated cylinders continued to consume power through frictional losses. Although some increase in efficiency was achieved, the design proved to be unreliable and was subsequently withdrawn from the market.
Multiple variable-throw eccentrics could also be harnessed in a variable-speed transmission. If the phase could be maintained constant as the eccentric varied from a maximum to zero, the phase would completely reverse upon passing through the null point. Thus, without changing pump valving, both forward and reverse speeds, as well as a neutral position, could be achieved with a signle set of variable-throw eccentrics.